The containers for containing liquid contents must be capable of favorably discharging the contents irrespective of the materials forming the containers. Discharging the content is not almost of a problem when the liquids having low viscosities such as water and the like are contained. Discharging the content, however, becomes a serious problem when the content is a highly viscous substance such as mayonnaise or ketchup irrespective of the plastic container or the glass container. Namely, the contents of this kind are not quickly discharged despite the container is tilted. Besides, the contents tend to stay on the container wall and cannot be all recovered. Particularly, the content stays in considerable amounts on the bottom of the container and is not all recovered.
In recent years, there have been proposed various kinds of technical arts for improving slipping properties to viscous substances by forming a liquid film on the surfaces of the formed bodies such as containers and the like (e.g., see patent documents 1 and 2).
According to the above technical arts, the slipping property can be strikingly improved as compared to the cases of adding an additive such as lubricant to the synthetic resin that forms the surfaces of the formed bodies, and attention has now been paid thereto.
According to the above means for improving surface properties by forming the liquid film on the surfaces of the substrates as described above, however, the life for effectively exhibiting the slipping property relying on the oil film does not last long. After the passage of long periods of time, therefore, the slipping property decreases and, depending upon the cases, the content adheres to the surfaces. This tendency becomes conspicuous particularly when the substance that falls down along the surface is an emulsified product containing water like a mayonnaise-like food.
There has, further, been proposed an art in which a liquid layer is formed on the inner surface of a container by using a liquid that exhibits slipping property to the content, and liquid protuberances are so formed as to locally protrude on the surface of the liquid layer in an attempt to greatly improve the slipping property to the content. This art has been patented already (patent document 3).
Though the above art is satisfactory from the standpoint of sustaining the slipping property, however, the resin layer that serves as the underlying layer for the liquid layer must be blended with a finely granular surface-roughening agent in order to form liquid protuberances on the surface of the liquid layer. That is, the inner surface of the container for constituting the liquid protuberances is formed relying on the granular surface-roughening agent in the underlying resin layer. Therefore, it is very difficult to control the surface roughness and the production thereof involves difficulty. Besides, viscous substances and, specifically, foods such as mayonnaise and ketchup are not, usually, all discharged and all spent at one time, but are discharged and spent in small amounts each time. Therefore, a further improved slipping property is required for these foods.
Further, the present applicant has previously proposed a packing material having a liquid film formed on the inner surface thereof that comes in contact with the content, the liquid film being dispersed with solid particles of a particle size of not larger than 300 μm (Japanese Patent Application No. 2014-126877).
In the above art previously proposed by the present applicant, however, sustenance of the slipping property has not been evaluated at all.